Vacuum-tube circuits and the like and method of controlling the same



Aug. 19, 1930. E. R. STOEKLE 1,773,503

VACUUM TUBE CIRCUITS AND THE LIKE AND METHOD OF CONTROLLING THE SAMEFiled Aug. 1925 W. 2 5.2. N 5 w Patented Aug. 19; 1930 UNITE D ,sT TESnnwnv 1a.. sr'oEKLrroF iyrinwnuxnni WISCONSIN i VACUUM-TUBE cmourrsfANnITHE LIKE AND rrnrnon on CONTROLLING 'rrrnv SAME Application file'dAugust; 7, 1925 j sri'a1 f1vo} 4s,76a 7 This invention relates toimprovements 'in vacuum tube circuits and'the like, and the method ofcontrolling the same, particularly with regard to circuits employed inradio communication. k

In an electrical circuit includingso-called negative resistance, itis-well known that the phase 1 relation between the voltage drop 'acrossthe resistance and the current through lathe resistanceis an importantfactor in determining whether or not the circuit will generateelectrical oscillations. a

The types of negative resistance devices commonly used in'circuits forradio com- ,15 munication usually employ three electrode thermionicvacuum tubes, electric are, or gaseous discharge devices. Since thethree electrode vacuum tube is most commonly used insuch circuits, thenew methodof oscillation control herein described, will referparticularly to the vacuum tube, although it is equallyapplicable toother types of negative resistance devices. I One object ofthisinventifo'n is to provide 2 an improved methodof controlling thetendency of the radio frequency tubes tooscill'ate in so-called radiofrequency amplifying-receivers. I f .j 1 Another object is to provide animproved ,130 method of controllingthe oscillation of an electricalcircuit including a negative resistance device. 1 I

Another object is to provide an improved method ofcontrollingtheoscillation of radio frequencyvacuum tubes whereby the range ofoscillation control .is greatly increased as compared to existingmethods. l

Another object is to :provide improved means whereby the inductance andthe re.-

I sistance in the plate circuit of a vacuum tube may be simultaneouslyvaried for the purpose of controlling electrical oscillationof thecircuit. v i f v, T

Another object is to provide animproved method of controlling thetransfer of oscillating energy between successive stages of a vacuumtube radio-frequency amplifier. H

Other objects and novel features of this improved method and means forcontrolling vacuum tube circuits, Will be apparent from Figure 1 showsdiagrammatically a radio receiving circuit employing a radio frequencythe following specifications and the accom pan ying dra'wingsf; g 1 1-Embodim ents"of 'the invention are shown in the accompanying drawingsin which 2- amplifier tube and a det'ector tube with the new m'ethodofoscillation control.

Figure 2 shows-diagrammatically.a two stageradio frequency amplifierwith the new method of oscillation control and a detector. Figure 3showsa single stage radio frequency amplifier and detector with the new'metho'dof oscillation control applied to the radio frequency-transformer,-' coupling the detector'tothe amplifier;

PATE T o mcrf f Referring to Figure l, the aerial 1 is coupled'to thegrid 2 of the first vacuum tube by m'eans'of the primary and secondarycoils 3' and4. The" variable 'condenser 5serves to tune thegrid circuitof the first tube. The

plate circuit of 'this'tube includes the inductive primary coil "6, theauxiliary coil 7-, resistance'8 and a fixed condenser 9.

v The secondary 1'0 of'the'above mentioned radio frequency transformeris tuned by 'me'ans ofa vfariable'condenser 11 and isconnectedithroughthe grid condenser 12 and grid leak1j8--to-the-grid '14 of the, detectortube. The battery 15 maintains the plates 24 and16 of the amplifiera'nddetector tube V respectively, a-t a positive potential with re--spect to the filaments 17 ,and.18. Battery 19 suppliesgthrough theresistance 2O a: current for heatingthe filaments. 17 and 18'; Telephonereceivers 21 :are connected to the plate circuit vofi the detector tubein 'the usual .ma e i e .op ra bnbfthe circuit shown in Fig;

ure 1, is as follows :Electr,ical oscillations received upontheaejrialare impressed upon the} grid 2- in theus ual manner. jTheseosci-llations cause corresponding variations in the electronjflow fromthe filamentl? to the plate 24;o'f the vacuum tube. These variationsinthe platecurrenti pass through coils 6 and 7 and through the condenser9,-back tothe fil'a-,

merit; portion ofj' 'the oscillating current isuhowever, divertedfromthe coil? via the resistance 8, the amount of such diversion 3 ofcurrent being dependent upon the position of the movable contact 22 onthe resistance 8. The condenser 9 is of sufficient capacity'to readilyallow the passage of high frequency current so that very little of suchcurrent will pass through the battery 15. Direct current is suppliedfrom the positive terminal of this battery through the resistancejS, 1n-

ductance 7 and coil 6 to the plate 24 of the vacuum tube. The negativeend of battery 15 is connected to the filament circuit inthe usualmanner. y p The resistance 8 is preferably non-inductive and may have avalue. of. the order of 200,000 ohms although the invention is notlimited to this value. It is also preferably-ta pered so that itsresistance per unit length decreases as the contact22 moves toward'thepoint 23. As the contact 22 approaches 23, the portion of the resistance8' in parallel with the coil 7 is progressively decreased, while theportion of resistance 8 in series with the .battery 15.,is progressivelyincreased. Therefore, the inductive value of coil 7, which is effectivein the oscillating plate circuit, is progressively decreased, while theresistance in series with the voltage supply 15 is increasech thusdecreasing the direct current voltage applied between the plate 24andthe filament 1?. 'It-is, therefore, apparent that a movement of thecontact 22 towards point23 produces a simultaneous decrease in theinductance effective in the oscillating circuit and in the directcurrent voltage applied between plate 24 and fila; ment 17. v

If the'vacuum tube generates oscillations at a given frequency with thecontact 22 at a position removed from 23, it will be found that as 22moves toward 23, the generation of oscillation at that frequency willgradually disappear. This disappearance of the gen: erated oscillationis due to two factors. First, a decrease in eifective inductancein theoscillating plate circuit'which changes the phase relation between thecurrent through the vacuum tube and the voltage applied. Second, adecrease in applied voltage so that the so-called capacity feed-backetween the plate 24 andthe grid 2 is decreased. It has been found thatthis simultaneous variation of the effective inductance in theoscillating circuit and of the direct current voltage impressed uponthis circuit produces a very smooth control of the oscillation of thetube over a'wide range of frequencies.

Figure 2 shows the same general principle of oscillation control appliedto a radio receiving circuitemploying two stages of tuned radiofrequency amplification and adetectorl The radio frequency. amplifyingtubes are shown respectively at 25 and 26 and the detector at 27. .Thegrid circuits of these tubes have inductive secondary coils 28, 2 9and30,

tuned by means of the variable condensers 31, 32 and 33, respectively.

The antenna coil is shown at 34 and the primary coils 35 and 36 areshown respectively in the plate circuits of the tubes 25 and 26. Thefilament battery 37 supplies heating current to each of the filaments ofthe vacuum tubes by means of conductors 38 and 39. The common conductor40 connects together the plate coils 35 and 36.

The auxiliary coil 41in series with the condenser 42, is connectedbetween the corn- 'mon conductor 40 and the common filament circuitconductor. 38. The battery 43 has its negative terminal connected to theconductor 38,- and its positive terminal connected throughthe'resistance 44 to the conductor 40. The variable contact 45, bearingon this resistance, is connected through the conductor 46 to theauxiliary coil 41. A somewhat lowervoltage is tapped from the battery 43by means of the conductor 47, which connects through thetelephonereceiversto the plate of the detector tube as shown.

I The operation of the circuit of Figure 2. is exactly similar to thatof Figure 1, except that the efiective inductance in the platecircuitsof the two tubes 25 and 26 is simultaneously varied bychangingthe location of the contact upon the resistance 44; and at thesame timea corresponding variation of the voltage impressed upon the plates ofthese tubes iseifected. As the contact 45 is moved towards 40, the partof the resistance 44, electrically in parallel with the coil 41, is

progressively decreased, thereby decreasing the inductance of the coil41 effective in the plate circuits of both the vacuum tubes 25 and 26.scribed decrease of effective inductance, there isa correspondingincrease of the resistance in series with the battery 43, therebydecreasing the'voltage upon the plate circuits of both the tubes 25and26. v

The principle of varying the inductance effective in the plate circuitsand at the same time varying the voltage impressed upon these circuits,is shown applied to one and twotubes in Figure land Figure2,respectively, but may be equally well applied to any desired. number ofradio frequency tubes.

Figure 3 shows a radio frequency amplifier tube 48 connected in cascadewith adetector 49 The antenna coil 50 is coupled to a grid coil 51 whichis tuned by means of a variable condenser- 52. The plate coil of thetube 48 has its windings in two sections 53 and 54. The conductors 55,56, 57 and 58 connect the plate coil in series with the condenser 59 andacross the filament and plate'of the tube 48. The resistance 60 isconnected by means of conductor 61 to a point on the plate coilintermediate the sections 53 and 54. The positive terminal of thebattery 62 is connected to the resistance 60 by. means of theCoincidently with the above de conductor 63. The negative terminal ofthis battery is connected to the common filament circuit as shown; Thesecondary coil 64 is inductively coupled to the composite plate. coilabove described and is tuned by means of the variable condenser 65. Thecontact 67is o movable upon the resistance 60 and is connected to theconductors 56 and 57 by means of a conductor 68. The telephone receiver66 is connected to the plate of the detector tube 49 and to thebattery62 in the usual manner.

The operation of the circuit described in Figure 3, differs somewhatfromthe operation of'thosedescribed in Figures 1 and 2, in that themutualinductance of the plate C011 and grid co l coupling successivevacuum tubes, is varied in addition to a variationof the self-inductionofthe plate coil. It is apparent from Figure 8 that the section 54: of

1 48 is decreased, and at the same timethe muincreased, the tendency forthe radio lire-IT the plate coil is shunted by a variable portion of theresistance 60. It is further apparent that as the resistance shuntingthe section varies, theremainder of the resistance 60,

which isin series with the battery 62,1varies in inverse proportion.Therefore, as theresistance shunting 54 is decreased, the inductanceeffective in theplate circuit of the tube tual inductance between theplat'e'coil of the tube 48 and the grid coil .64 will also be decreasedCoincident with the above described decrease in self and mutualinduction, there fwill be a corresponding decrease in the voltageeiiective between the plate and filamentof tube 48. Thisis due to theincrease of the part of resistance in series with thebats tery 62. r

It is well known that as the'natural f requency to'which thegridcircuits of a multi stage radio frequency amplifier arejtuned isquency tubes to generate oscillations increases. It is further wellknown thatas the above mentioned natural frequency decreases,

the transfer of energy between successivestages through their mutualcoupling also decreases These factors all tend to facilitate thegeneration of oscillations in the amplifier circuits.

The method of control disclosed in Figure 3 governsthe generation ofoscillations by varying theself-induction in the plate coil of theamplifier tube, themutual inductance of thiscoil with respect to thegrid coil of I thenext tube, and the voltage impressed upon the plate ofthe amplifier. The simultaneous control. of these factors by the circuitarrangeoment shown, provides aconvenient'method vices having similarcharacteristics, may be employed without departing "from the spirit i a1 V i a v V: 1. In an electrical circuit, includingan orscope,ofthisiiivention-as set forth in the following claimsr- ,o r

electrical discharge device, a source, of voltage in series with saiddevice, an inductance coil in series with said device, an auxiliaryinductance coil also" in series with said device,.aresistance having-avariable portion o in parallel with Fsa'id secondmentioned coil,

the remainder of said resistance being in 1 series with said voltagesource, meansfor lvarying the i'portionof said resistance in par.-

allel with said second mentioned coil and the i, so

portion in series with said voltage source,

in [inverse "relation, whereby the inductance of said second C011effective in said circuit, and the voltage mpressed upon said electricaldischarge device may be simultaneously varied.

2. In, an electricalcircuit, includingan electricaldischarge device, asource of voltk age in series with said device an inductance coil inseries with-said device, an auxiliary inductance coil also in serieswith said device, an electrical condenser in parallel with said deviceand both otsaid coils, a resistance having a variable portion inparallel with said resistance being in series with said voltage source,means for varying the portion .95 said secondmentioned coil, theremainder of of said resistance in parallel with-said second mentionedcoil and the portion in series with said voltage source,1in inverserelation, whereby the inductanceof said second coil. effective in saidcircuit, Iandthe v-oltagefimpressed upon said electricaldischarge'device may be simultaneously varied.

3. Anelectrical circuit, including a vacuum tube, an inductance coil'inseries with the plate of said tube, a second inductance coil in serieswith said first mentioned'coil,

an electrical condenser in parallel with said. coils and said tube, aresistance in series Wlth said first mentioned coil and a source ofvoltage, acommon connection for said first and said second mentionedcoils and said resistance, a contact movable upon said resistanoe forconnectingthe common'terminal of said second mentioned coil and saidcondenser to a variable 'portionof said resist ance, whereby the portionof said resistance, in parallelwith' said second mentioned 'coil and theportion in series with said voltage 1 source may be vvaried ininverserelationand a simultaneous ,VallaillOIl of the inductance pressedon'said circuit may be accomplished.

effective in said circuit and the voltage im 4:. An electrical circuitincluding a three electrode vacuum tube, having a tuned grid circuit, aplate to filament-circuit, including a main coil, an auxiliary coil anda condenser, avresistancehaving oneter'mina-l con- 'nected to the commonconnection between said coils, and another terminal connected toa sourceof voltage, a variable contact upon said resistance, said contact beingcon- I nected to the common terminal of said auxiliary coil and saidcondenser, whereby a varying'portion of said resistance may be connectedin parallelwith said auxiliary coil and an inversely varying portion ofsaid resistance may be connected 1n series with said voltage source, forthe purpose of controlling the generation of oscillations by said vacuumtube. V

In testimony that I claim the foregoing I have hereunto set my hand atMilwaukee,

in the county. of Milwaukee and State of 7 Wisconsin.

ERWIN .R. STOEKLE.

